In the recent drive for higher integration and operating speeds in LSI devices, it is desired to miniaturize the pattern rule. Great efforts have been devoted for the development of the micropatterning technology using deep-ultraviolet (deep-UV) or vacuum-ultraviolet (VUV) lithography. The photolithography using KrF excimer laser (wavelength 248 nm) as the light source has already established the main role in the commercial manufacture of semiconductor devices. The photolithography using ArF excimer laser (wavelength 193 nm) has commenced commercial manufacture as the advanced microprocessing process. In the ArF excimer laser lithography, a further improvement in resist material performance is strongly demanded to enable a further extension of resolution, partially because the succeeding technology remains uncertain. Efforts have also been made on the development of the immersion lithography designed to extend the resolution by interposing a high refractive index liquid between a resist coating and a projection lens, and a resist material suited for the immersion lithography is thus needed.
The requisite properties for the resist materials adapted for the ArF excimer laser lithography include transparency at wavelength 193 nm and dry etch resistance. Resist materials comprising as a base resin poly(meth)acrylic acid derivatives having bulky acid-labile protective groups as typified by 2-ethyl-2-adamantyl and 2-methyl-2-adamantyl groups were proposed as having both the properties (JP-A 9-73173 and JP-A 9-90637). Since then, a variety of materials have been proposed. Most of them commonly use resins having a highly transparent main chain and a carboxylic acid moiety protected with a bulky tertiary alkyl group.
While the prior art resist materials for the ArF excimer laser lithography suffer from several problems, a decline of resolution by over-diffusion of the acid generated by the photoacid generator is a serious problem. In the ArF excimer laser lithography, the acid generated upon exposure triggers deprotection reaction on the base resin which proceeds during heat treatment following exposure (post-exposure bake or PEB). Movement or diffusion of the acid occurs during PEB. Since chemically amplified resist materials depends on the function of the acid to act as a catalyst to promote deprotection reaction, moderate acid movement is necessary. However, acid movement degrades an optical image, indicating that excess acid movement detracts from resolution. To comply with the outstanding demands for a further size reduction in the ArF excimer laser lithography including and a higher resolution due to a good command of the immersion lithography, there is a need for a resist material featuring controlled acid movement and higher resolution capability.